Lift mast assemblies frequently utilize rollers for guiding the mast uprights, carriage and lift chains for smooth low effort operation.
When used as a guide roller, for example side thrust or fore-aft, the roller must have an adjustment provision to enable proper radial positioning of the roller relative to the upright member against which it bears.
Frequently, the guide rollers are mounted on an eccentric shaft which is in turn connected to a shaft having an axis offset from the eccentric shaft axis. This shaft in turn is connected to the carriage, when used as a side thrust roller, and rotated relative to the carriage for radial adjustment purposes. An example of such a roller assembly is shown in U.S. Pat. No. 4,019,786 to William T. Yarris dated Apr. 26, 1977.
Typically, assemblies of this type are secured to a carriage support member, at a selected rotational position of the eccentric shaft and retained there in an assortment of different ways. U.S. Pat. No. 4,019,786 teaches the use of a threaded shaft, nut and washer for retention thereof, and U.S. Pat. No. 3,467,450 to H. K. Schmidt et al. dated Sept. 16, 1969 teaches the use of a pair of mating tapered surfaces and a threaded fastener for retention thereof.
These methods of retention have had only limited success since they rely on friction and clamping forces which are passive retention methods. When inadvertent loosening occurs improper adjustment results which reduces the efficiency of operation of the lift mast and ultimately results in premature wear of the roller, its associated componentry and damage to the lift mast.
Lift chains are utilized in lift masts to connect a moveable member, such as a carriage or moveable upright to a fixed upright and a lift jack. Usually the chain(s) is connected at one end to the fixed upright, trained over the sheave (roller) and connected at the other end to the moveable member. Typically, one end of the chain is connected by an adjustable member to provide adjustment of the chain tension. When a pair of chains are used equalization of the length and thus the tension is highly desirable to provide smooth, quiet and efficient operation. U.S. Pat. Nos. 4,280,592 to Richard J. Bartow dated July 28, 1981 and 4,238,004 to Harlan D. Olson dated Dec. 19, 1980 teach this type of chain arrangement.
Although this arrangement prevents tension adjustment, accessibility is often poor, inadvertent loosening frequent and accurate adjustment improbable due to friction between the rotatable sheave and the chain inhibiting sliding motion thereof.
Therefore, it would be advantageous to eliminate the adjustable device at the chain end connection and provide an adjustable sheave (roller) which would permit ease of chain tension adjustment throughout its full length and positive locking of the sheave to prevent inadvertent loosening.